1. Field of the Invention
Olefin-dicarboxylic anhydride copolymers and their ester derivatives are filtration aids in solvent dewaxing of waxy lubricating oils.
2. Prior Art
Copolymers of olefins and maleic anhydride, along with their ester and amide derivatives, have been taught as useful additives for various types of oils. For example, U.S. Pat. No. 3,413,104 teaches copolymers of C.sub.8 to C.sub.30 olefin with maleic anhydride which can then be amidated with polyamines to form a detergent additive for distillate fuel oils. U.S. Pat. No. 3,449,236 teaches as a dewaxing aid, a copolymer of C.sub.6 to C.sub.28 diolefin with maleic anhydride which is then esterified or amidated with a C.sub.12 to C.sub.30 alcohol or amine. U.S. Pat. Nos. 3,051,562 and 3,115,483 teach jet fuel containing a copolymer of maleic anhydride and C.sub.2 to C.sub.20 olefin reacted with a C.sub.4 to C.sub.20 alcohol and then with polyamine as a stabilizer. More recently, copolymers of C.sub.20+ olefins with maleic anhydride esterified with C.sub.20+ alcohols have been taught as fluidity improvers in various types of liquid hydrocarbons boiling from about 75.degree. F. to about 1,000.degree. F., including distillates, crudes and residual oils as taught by Dutch Application No. 69/13277.